Topic: Only firing on #2 & #3 pistons: Is it my slows? SOLVED!!!

[Hondalubr]

  1978 CB 750F is the model, and I already cleaned the carbs with the help of my other post. Now it is only firing on the 2 center plugs. I have spark to all 4 but the 1 & 4 pipes are warm not hot after running at idle (1400RPM) for about 10 minutes. The other 2 are hot as h311. I have tried to adjust the air flow screw in the front of the carb right next to the bowl. That seems to be the only adjustment screws there are on my model bike unless you remove the tops of the carbs and adjust the needles. Could I have not gotten out all of the gook in the slows? And by the way... Which or where are the slows on these carbs?  I think they are pressed in... is this right?  They didn't have a slot for a screwdriver and I didn't remove them when I cleaned the carbs. Also, are you supposed to be able to run a fine wire all the way through them to the top or throat?  I really don't understand slows, so if you could point me in the right direction on this it would help me alot. 
Thanks,
Hondalubr (Mike D.)

[TwoTired]

The slow jets have a .015 inch hole buried deep in them that can be difficult to clean.  Although they are pressed in, they can be yanked, cleaned and tapped back into place.

You carbs have an idle mixture screw theat meters fuel.  They are not airflow screws.  Sounds like your information is from a Clymer book that doesn't cover your model carbs.

The adjustment under the tops of the carbs are for synching the slides so each carb feeds the same volume of air to each cylinder.  The needles are attached to the slides.  And, to adjust them you need to remove the slides from the carbs.  The needles have notches in them for an E clip that sets their depth relative to slide position.  This allows for different airfuel mix ratios metered between 1/4 and 3/4 throttle settings.  Some needles have multiple grooves, but I'm not sure the 78 CB750 F model has more than one.
Cheers,

[Zeke]

Hey HL:

Likely you may have an ignition problem, not a jet problem.

When I rebuilt my bike this year I had the same problem -- a bad wiring repair by a PO was now intermittent.  so, 2 and 3 were firing because they are on the same coil -- 1 and 4 were'nt firing much.  It's funny, it was tough to figure out they weren't firing, because it idled OK.

Also, when I checked spark without the plugs in they were firing -- but not good enough.

They are warm because either firing once in a while or just conducting heat from the other firing pistons.

After I fixed the wiring it was all good again.  You should test your coil by swapping them -- if the other pipes are now cool you know it's the coil.  If not, could be points .......

Good Luck

Zeke

[Buffo]

when you remove the slows...DO NOT wobble them side to side!!!! Twist and pull straight up. Make sure when you reinstall them you get the straight right from the start. Mke sure you clean the slow air passage too.

to make sure they are flowing good take the red straw you  get with carb cleaner in a can and file one end to a point. I use a dremel tool. this way you can stuff it in the jet and air passage holes with no leaks...make sure when you squirt the cleaner thru them that they all squirt the same. squirt them all...if one squirts different amounts tht the others...clean it...carefull with the wire

[Hondalubr]

Likely you may have an ignition problem, not a jet problem.

Zeke,
Thanks for the advice. I swapped coils like you said, and it still was only hitting on the 2 & 3 cylinders. I spent the afternoon/evening re-cleaning the carbs by pulling them off once again and disassembling everything "AGAIN" and this time paid more attention to the slows. I removed them like you said in my other post. I used a very small diameter straight pin very carefully until I could use a small diameter hose about 6inches long and then blew into it. once all of the jets were "blowing" at what seemed to be the same rate with the same pressure, I reassembled the carbs and started the bike. All 4 cylinders are now firing correctly! I do hav a low idle miss but once it hits about 2000 RPMs it smoothes right out. I took it for a spin around the neighborhood, never more than 1/2 mile away from home and got it up to about 55MPH for about 30 seconds before I needed to slow down for a curve. It was pretty smooth, and the throttle responded pretty good too. I never stalled like I did before. Even when I came to a stop sign, or up my driveway without having to open the throttle and feather it to keep it started. I could cruise with very little throttle unlike before as well. It's not correct but I am getting closer. At least I am running on all 4 now.

Buffo The Egotistical & Stupid, LOL, That name has to go! I like Buffo much better!

I read the thread that made you mad enough to change your sign in. That guy had no right nor the reason to say you were stupid! I have read your posts and find them not only entertaining but also quite informative. I gained a lot of respect for you in one of your posts when you were talking about your responsibilities to your family and your employees.
I found the post and coppied it here below:
Buffo Wrote:
"I have said the same thing to many people. However I have the livelyhood of a good number if employees to think about, not to mention my own family.

I have one guy inpeticualr (<--look at that spelling) who is 19, 2 year old boy and a wife. He pays his bills thru me.

I have a bunch of them. I dont go to work, they dont get to work...they dont get paid.

Add to that all the bills that come with employees...ins., workers comp, ...unemployment ins... but I like being a GOOD employer. Maybe I'm not the nicest or most understanding but I do offer health ins."


You can tell a lot about a man by the way he runs a business and speaks so highly of his responsibilities, IE Family and employees, putting them before his own pleasure, while at the same time making the time for ones hobbies.
Thank you for your reply to my post. I had already worked on my bike before getting the chance to read it, but your take on my situation was right on.

Thanks guys,
Hondalubr (Mike D.)

[Buffo]

I am glad your bike worked out ok.

And thanks for the....review

[dusterdude]

gee don,now he thinks you`re a nice guy

[eldar]

just to clarify, the 78K & F do NOT have slots in the needle, if they are original.

[Hondalubr]

Yeah there are no slots in mine. I figured it out when I took apart the assembly. But now its running great. I can't wait to get it registerred and I get my licence so I can ride it all over.
Mike